Organic electroluminescent display device

ABSTRACT

An organic electroluminescent display device comprises a substrate including a display region, and a pad region in a periphery of the display region, the display region including a pixel region; a gate pad, a data pad and a power pad in the pad region, the gate pad, the data pad and the power pad electrically connected to a gate line, a data line and a power line, respectively; a first electrode in the pixel region, the first electrode connected to the driving thin film transistor; an organic electroluminescent layer on the first electrode; a second electrode over an entire surface of the substrate including the organic electroluminescent layer; a dummy pad in the pad region, the dummy pad electrically connected to at least one of the power line and the second electrode; and a ground pad in the pad region, the ground pad electrically connected to the second electrode.

The present invention is a divisional application of copendingapplication Ser. No. 11/023,605, filed on Dec. 29, 2004, now U.S. Pat.No. 7,348,605 which claims the benefit of Korean patent Application No.2003-0099858 filed in Korea on Dec. 30, 2003, which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device, and moreparticularly, to an organic electroluminescent display (OELD) device.

2. Discussion of the Related Art

In general, an OELD device emits light by injecting electrons from acathode and injecting holes from an anode into an emission layer,combining the electrons with the holes, generating excitons, andtransitioning the excitons from an excited state to a ground state.Unlike liquid crystal display (LCD) devices, an OELD does not require anadditional light source to emit light since the transition of theexcitons between the excited and ground states causes light emission.Accordingly, the size and weight of the OELD device is less than that ofan LCD device. In addition, the OELD device has low power consumption,superior image brightness, and fast response time. Thus, the OELDdevices are employed in consumer electronic applications, such ascellular phones, car navigation systems (CNS), personal digitalassistants (PDA), camcorders, and palmtop computers. Moreover, sinceOELD devices are manufactured using a relatively simple fabricationprocess, OELD production costs much less than LCD.

There are currently at least two different types of OELD devices:passive matrix OELD devices and active matrix OELD devices. Although thepassive matrix OELD devices have simple structures and are formed bysimple fabrication processes, passive matrix OELD devices require arelatively high amount of power to operate. In addition, the displaysize of passive matrix OELD devices is limited due to their structure.Furthermore, as the number of conductive lines increases in a passivematrix OELD device, an aperture ratio of the passive matrix OELD devicesdecreases. On the other hand, active matrix OELD devices have a highemission efficiency and can produce high-quality images for largerdisplays with relatively low power consumption.

FIG. 1 is a cross-sectional view of an OELD device according to therelated art. Referring to FIG. 1, an OELD device 10 includes first andsecond substrates 12 and 28 that are spaced apart from each other andbonded together using a sealant 26. The first substrate 12 includes anarray element layer 14 having a thin film transistor (TFT) T formed onan inner surface of the first substrate 12. A first electrode 16, anorganic electroluminescent (EL) layer 18, and a second electrode 20 aresequentially formed on the array element layer 14. The organic EL layer18 may include red, green, and blue emission layers to displayfull-color images. Each of the red, green, and blue emission layers maybe disposed in each pixel region P. The second substrate 28 includes amoisture absorbent desiccant 22 that eliminates moisture and oxygen thatmay penetrate the organic EL layer 18. The moisture absorbent desiccant22 is disposed within an etched portion of the second substrate 28, andis fixed by a holding element 25.

FIG. 2 is a plan view of an array element layer of an OELD deviceaccording to the related art. Referring to FIG. 2, the array elementlayer 14 (shown in FIG. 1) includes a switching thin film transistorT_(S), a driving thin film transistor T_(D), and a storage capacitorC_(ST) formed on a transparent insulating substrate 12, such as glass orplastic. The switching thin film transistor T_(S) and the driving thinfilm transistor T_(D) may include a combination of at least one TFT. Inaddition, a gate line 32 and a data line 34 crossing each other areformed on the substrate 12. A pixel region P is defined by a crossing ofthe gate line 32 and the data line 34. An insulating layer (not shown)is interposed between the gate line 32 and the data line 34. A powerline 35 is disposed parallel to and spaced apart from the data line 34and also crosses over the gate line 32.

In FIG. 2, the switching thin film transistor T_(S) includes a switchinggate electrode 36, a switching active layer 40, a switching sourceelectrode 46, and a switching drain electrode 50. Similarly, the drivingthin film transistor T_(D) includes a driving gate electrode 38, adriving active layer 42, a driving source electrode 48 and a drivingdrain electrode 52. The switching gate electrode 36 is connected to thegate line 32, and the switching source electrode 46 is connected to thedata line 34. The switching drain electrode 50 is connected to thedriving gate electrode 38 via a first contact hole 54. The drivingsource electrode 48 is connected to the power line 35 via a secondcontact hole 56. In addition, the driving drain electrode 52 isconnected to a first electrode 16 at the pixel region P. The power line35 overlaps a first capacitor electrode 15. An insulating layer isinterposed therebetween to form the storage capacitor C_(ST).

Although not shown, a gate pad, a data pad and a power pad are disposedin a pad region in a periphery region of a display region transmittinglight. The gate pad, the data pad and the power pad are formed in endportions of the gate line, the data line and the power line,respectively. Further, a ground signal is applied to a ground pad and itis disposed in one of the portions corresponding to the gate, the dataand the power pads. In general, the power pad and the ground pad aredisposed in their respective areas in the pad portions. Therefore,current or carrier may flow in a certain direction, so that anon-uniform image quality occurs due to a resistance deviation in alarge size model different from a small size model.

FIG. 3 is a plan view of an OELD device according to the related art.Referring to FIG. 3, a substrate 12 is prepared with a display region DDand a pad region PP in a periphery of the display region DD. The padregion PP includes first to fourth pad regions PP1 to PP4. The first padregion PP4 is disposed adjacent to the second pad region PP2. A gate pad60, a data pad 50, a power pad 70 and a ground pad 80 are formed in thefirst to fourth pad regions PP1 to PP4, respectively. For example, agate signal, a data signal, a power signal and a ground signal areapplied to the gate pad 60, the data pad 50, the power pad 70 and theground pad 80 through tape automated bonding, respectively.

The first electrode 16 (shown in FIG. 1) in the pixel region P (shown inFIG. 1) is connected to the driving thin film transistor T_(D) (shown inFIG. 2), the organic electroluminescent layer 18 (shown in FIG. 1) isdisposed on the first electrode 16, and the second electrode 20 (shownin FIG. 1) is disposed over the entire surface of the substrate 12having the organic electroluminescent layer 18. The electric potentialof the second electrode 20 can be maintained by applying a commonvoltage through the ground pad 80.

For example, the second electrode 20 and the ground pad 80 are connectedto each other via a first contact hole 27 in the display region DD andthe ground pad 80 is connected to an external circuit (not shown) via asecond contact hole 29 in the pad region PP. It should be noted that amoving direction 90 of the carriers or current is from the power pad 70to the ground pad 80. Therefore, the power pad 70 may be defined as apad where a flow of carriers or current begins, and the ground pad 80may be defined as a pad where the flow of the carrier or current ends.

In other words, carrier or current flows along one direction from in thethird pad portion PP3 to the fourth pad portion PP4. Consequently, whenthis arrangement structure for the pad region PP is applied to a smallsize OELD model, a resistance deviation can be reduced because of thesmall size of the OELD. Therefore, image quality problems do not occurin all regions of the OELD. However, the bigger the size of the OELDpanel, the lower the image quality.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to organicelectroluminescent display device that substantially obviates one ormore of the problems due to limitations and disadvantages of the relatedart.

An object of the present invention is to provide an OELD device having auniform image quality.

Another object of the present invention is to provide a dual panel typeOELD device having a uniform image quality.

Additional features and advantages of the invention will be set fourthin the description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, an organicelectroluminescent display device includes a substrate including adisplay region, and a pad region in a periphery of the display region,the display region including a pixel region; a gate line, a data linecrossing the gate line, and a power line on the substrate in the displayregion, the power line crossing one of the gate line and the data line;a switching thin film transistor and a driving thin film transistor inthe pixel region, the switching thin film transistor connected to thegate line and the data line, and the driving thin film transistorconnected to the switching thin film transistor and the power line; agate pad, a data pad and a power pad in the pad region, the gate pad,the data pad and the power pad electrically connected to the gate line,the data line and the power line, respectively; a first electrode in thepixel region, the first electrode connected to the driving thin filmtransistor; an organic electroluminescent layer on the first electrode;a second electrode over an entire surface of the substrate including theorganic electroluminescent layer; a dummy pad in the pad region, thedummy pad electrically connected to at least one of the power line andthe second electrode; and a ground pad in the pad region, the ground padelectrically connected to the second electrode.

In another aspect, an organic electroluminescent display device includesa substrate including a display region, and first to fourth pad regionsin a periphery of the display region, the display region including apixel region, the first pad region adjacent to the second pad region,the first pad region facing the third pad region; a gate line, a dataline crossing the gate line, and a power line on the substrate in thedisplay region, the power line crossing one of the gate line and thedata line; a switching thin film transistor and a driving thin filmtransistor in the pixel region, the switching thin film transistorconnected to the gate line and the data line, and the driving thin filmtransistor connected to the switching thin film transistor and the powerline; a gate pad and a data pad in at least one of the first to fourthpad regions, the gate pad and the data pad electrically connected to thegate line and the data line, respectively; a second substrate facing andspaced apart from the first substrate, the second substratecorresponding to the display region of the first substrate; a firstelectrode on an entire surface of the second substrate; an organicelectroluminescent layer on the first electrode; a second electrode onthe organic electroluminescent layer in the pixel region; a connectionelectrode connecting the second electrode and the driving thin filmtransistor, the connection electrode between the first substrate and thesecond substrate; a plurality of dummy pads electrically connected tothe power line, the plurality of dummy pads including a first dummy padin the first pad region and a second dummy pad in the second pad region;and a ground pad in the third pad region, the ground pad electricallyconnected to the first electrode.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a cross-sectional view of an OELD device according to therelated art.

FIG. 2 is a plan view of an array element layer of an OELD deviceaccording to the related art.

FIG. 3 is a plan view of an OELD device according to the related art.

FIG. 4A is a plan view of a display region and a pad region in anexemplary OELD device according to an embodiment of the presentinvention.

FIG. 4B is a plan view of a pixel region in an exemplary OELD deviceaccording to an embodiment of the present invention.

FIG. 5 is a magnified view for portion V shown in FIG. 4A.

FIG. 6 is a cross-sectional view of an exemplary dual panel OELD deviceaccording to an embodiment of the present invention.

FIG. 7 is a plan view of a display region and a pad region in anexemplary dual panel OELD device according to an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

FIG. 4A is a plan view of a display region and a pad region in anexemplary OELD device according to an embodiment of the presentinvention. FIG. 4B is a plan view of a pixel region in an exemplary OELDdevice according to an embodiment of the present invention.

Referring to FIGS. 4A and 4B, a substrate 100 includes a display regionDD and a pad region PP in a periphery of the display region DD. Althoughnot shown, the display region DD includes a plurality of pixel regionsdisposed on the substrate 100. A pixel region includes a gate line 102,a data line 104 crossing the gate line 102, and a power line 106crossing one of the gate line 102 and the data line 104. Further, aswitching thin film transistor Ts is connected to the gate line 102 andthe data line 104, and a driving thin film transistor T_(D) is connectedto the switching thin film transistor Ts and the power line 106 in thepixel region P.

A gate pad 120, a data pad 122 and a power pad 124 are disposed in thepad region PP. The gate pad 120, the data pad 122 and the power pad 124are electrically connected to the gate line 102, the data line 104 andthe power line 106, respectively. A first electrode 130 is connected tothe driving thin film transistor T_(D) in the pixel region P. An organicelectroluminescent layer (not shown) is formed on the first electrode130, and a second electrode 134 is formed over the entire surface of thesubstrate 100 having the organic electroluminescent layer.

A dummy pad DP is disposed in the pad region PP. The dummy pad DP iselectrically connected to at least one of the power line 106 and thesecond electrode 134. For example, the dummy pad DP includes a firstdummy pad DP1 and a second dummy pad DP2. In addition, a ground pad 150is disposed in the pad region PP. The ground pad 150 is electricallyconnected to the second electrode 134.

The pad region PP includes first to fourth pad regions PP1 to PP4. Asshown in FIG. 4A, the first pad region PP1 is disposed adjacent to thesecond pad region PP2. The gate pad 120 and the first dummy pad DP1 aredisposed in the first pad region PP1. The data pad 122 and the seconddummy pad DP2 are disposed in the second pad region PP2. The power pad124 is disposed in a third pad portion PP3. The ground pad 150 isdisposed in the fourth pad portion PP4. Power signals are applied to thefirst and second dummy pads DP1 and DP2, respectively.

Although not shown, a power signal and a ground signal may be applied tothe first dummy pad DP1 and the second dummy pad DP2, respectively.Conversely, a power signal and a ground signal may be applied to thesecond dummy pad DP2 and the first dummy pad DP1, respectively.Additionally, the ground signal may be applied to the dummy pad DPhaving the first and second dummy pads DP1 and DP2. However, one of thefirst and second dummy pads DP1 and DP2 may be omitted.

Although not shown, the dummy pad DP is electrically connected to anexternal circuit (not shown) by tape automated bonding. For example,when the first electrode 130 acts as an anode, it may include indium tinoxide. On the other hand, when the second electrode 134 acts as acathode, it may include one of aluminum (Al), calcium (Ca), magnesium(Mg) and lithium fluorine/aluminum (LiF/Al).

A first contact hole 162 is disposed in the display region DD to connectthe second electrode 134 and the ground pad 150. A second contact hole164 is disposed in the pad region PP to connect the ground pad 150 andthe external circuit. In other words, a ground signal is applied toground pad 150 through the external circuit. A seal pattern 170 isdisposed between the display region DD and the pad region PP. Althoughnot shown, the OELD device according to an embodiment of the presentinvention further includes another substrate or a passivation layer forencapsulation of the OELD device.

FIG. 5 is a magnified view for portion V shown in FIG. 4A. Referring toFIG. 5, although the first dummy pad DP1 is disposed in the same padregion PP as the gate pad 120, a gate signal is not applied to the firstdummy pad DP1. One of a power signal and a ground signal is applied tothe first dummy pad DP1. A signal applied to the dummy pad DP (shown inFIG. 4A) may be defined as follows.

According to an embodiment of the present invention, the display regionDD may include a plurality of gate pads 120, a plurality of data pads122, a plurality of power pads 124, a plurality of ground pads 150 and aplurality of dummy pads DP. However, these conditions may be changed inaccordance with the presence of the power pad 124 and the ground pad 150or in accordance with the size of the power pad 124 and the ground pad150. In an embodiment of the present invention, an ELD device having thedummy pad can be manufactured with a large size and provide a uniformimage quality.

FIG. 6 is a cross-sectional view of an exemplary dual panel OELD deviceaccording to an embodiment of the present invention. FIG. 7 is a planview of a display region and a pad region in an exemplary dual panelOELD device according to an embodiment of the present invention.Referring to FIGS. 6 and 7, a first substrate 200 includes a displayregion DD and a pad region PP in a periphery of the display region DD.The display region DD includes at least one pixel region P. Although notshown, a gate line, a data line crossing the gate line, and a power linecrossing one of the gate line and the data line are disposed on thefirst substrate 200 in the display region DD. A switching thin filmtransistor (not shown) is connected to the gate and data lines. Adriving thin film transistor T_(D) is connected to the switching thinfilm transistor and the power line 206 in the pixel region P. A secondsubstrate 300 faces and is spaced apart from the first substrate 200.Although not shown, the second substrate 300 corresponds to the displayregion DD of the first substrate 200. A first electrode 304 is formed onthe entire surface of the second substrate 300. An organicelectroluminescent layer 306 is formed on the first electrode 304. Asecond electrode 308 is formed on the organic electroluminescent layer306 in the pixel region P.

When the first electrode 304 acts as an anode, it may include indium tinoxide. When the second electrode 308 acts a cathode, it may include oneof aluminum (Al), calcium (Ca), magnesium (Mg) and lithiumfluorine/aluminum (LiF/Al). The first electrode 304, the organicelectroluminescent layer 306 and the second electrode 308 form anorganic electroluminescent diode D_(EL).

An auxiliary first electrode 302 is formed between the second substrate300 and the first electrode 302 at a boundary of the pixel region P tolower resistivity of the first electrode 302 acting as the anode.Further, a connection electrode 320 connects the second electrode 300and the driving thin film transistor T_(D). The connection electrode 320is disposed between the first and second substrates 200 and 300. A sealpattern 350 is disposed between the display region DD and the pad regionPP to attach the first substrate 200 and the second substrate 300.

Although not shown, a power signal is applied to the power line and thesecond electrode 308 is electrically the power line through the drivingthin film transistor T_(D). At this time, the power signal is applied tothe power line through the dummy pad DP without a power pad. The organicEL layer 306 may include red, green, and blue emission layers to displayfull-color images. Each of the red, green, and blue emission layers maybe disposed in each pixel region P. Carriers or current move in variousdirections 358 in the display region, as shown in FIG. 7, therebyimproving image quality.

A gate pad 230 and a data pad 240 are formed in the pad region PP. Thegate pad 230 and the data pad 240 are electrically connected to the gateline and the data line, respectively. A dummy pad DP is formed in thepad region PP. The dummy pad DP is electrically connected to the powerline. A ground pad 250 is formed in the pad region PP. The ground pad250 is electrically connected to the first electrode 304. The pad regionPP includes first to fourth pad regions PP1 to PP4. The first pad regionPP1 is disposed adjacent to the second pad region PP2.

The dummy pad DP includes a first dummy pad DP1 in the first pad regionPP1 and a second dummy pad DP2 in the second pad region PP2. The gatepad 230 and the data pad 240 are disposed in the first pad region PP1and the second pad region PP2, respectively. The ground pad 250 isdisposed in one of the third and fourth regions PP3 and PP4. Forexample, the data pad 240 is further disposed in the third pad regionPP3 facing the second pad region PP2, and the third dummy pad DP3 isalso disposed in the third pad region PP3. In this case, the ground pad250 is disposed in the fourth pad region PP4. Although not shown, thedummy pad DP is electrically connected to an external circuit by tapeautomated bonding.

As explained above, a power signal may be applied to at least two of thefirst to third pad regions, thereby reducing a resistance deviation dueto a dominant direction of carriers or current. Accordingly, a largesize dual panel type OELD having a uniform image can be manufactured.

In accordance with embodiments of the present invention, a high apertureratio may be obtained in a top emission-type OELD device. In addition,an array element layer including a TFT and an organic EL diode may beindependently formed on respective substrates. Thus, undesired effectsdue to fabrication processes of the organic EL diode may be prevented,thereby improving overall production yield. Furthermore, resistancedeviation is reduced by applying at least one of a power signal and aground signal to a dummy pad in the pad region, which includes one ofthe gate pad and the data pad. Thus, a large size OELD device having auniform quality can be manufactured.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the organicelectroluminescent display device of the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. An organic electroluminescent display device, comprising: a substrateincluding a display region, and first to fourth pad regions in aperiphery of the display region, the display region including a pixelregion, the first pad region adjacent to the second pad region, thefirst pad region facing the third pad region; a gate line, a data linecrossing the gate line, and a power line on the substrate in the displayregion, the power line crossing one of the gate line and the data line;a switching thin film transistor and a driving thin film transistor inthe pixel region, the switching thin film transistor connected to thegate line and the data line, and the driving thin film transistorconnected to the switching thin film transistor and the power line; agate pad and a data pad in at least one of the first to fourth padregions, the gate pad and the data pad electrically connected to thegate line and the data line, respectively; a second substrate facing andspaced apart from the first substrate, the second substratecorresponding to the display region of the first substrate; a firstelectrode on an entire surface of the second substrate; an organicelectroluminescent layer on the first electrode; a second electrode onthe organic electroluminescent layer in the pixel region; a connectionelectrode connecting the second electrode and the driving thin filmtransistor, the connection electrode between the first substrate and thesecond substrate; a plurality of dummy pads electrically connected tothe power line, the plurality of dummy pads including a first dummy padin the first pad region and a second dummy pad in the second pad region;and a ground pad in the third pad region, the ground pad electricallyconnected to the first electrode.
 2. The device according to claim 1,wherein the gate pad and the data pad are disposed in the first padregion and the second pad region, respectively.
 3. The device accordingto claim 2, wherein the data pad is further disposed in the fourth padregion facing the second pad region.
 4. The device according to claim 3,wherein the plurality of dummy pads includes a third dummy pad disposedin the fourth pad region.
 5. The device according to claim 1, whereinthe dummy pads are electrically connected to an external circuit by tapeautomated bonding.
 6. The device according to claim 1, wherein the firstelectrode acts as an anode.
 7. The device according to claim 6, whereinthe first electrode includes indium tin oxide.
 8. The device accordingto claim 1, wherein the second electrode acts as a cathode.
 9. Thedevice according to claim 8, wherein the second electrode includes oneof aluminum (Al), calcium (Ca), magnesium (Mg) and lithiumfluorine/aluminum (LiF/Al).
 10. The device according to claim 1, whereinthe dummy pads are electrically connected to the second electrodethrough the power line.